Summary The recent rise in adolescent vaping of nicotine could increase future rates of alcohol use disorder (AUD). Epidemiological and animal studies find that adolescent exposure to nicotine increases ethanol consumption in adulthood. This long-term increase in ethanol consumption is not found following similar exposure to nicotine in adulthood, indicating adolescence is a uniquely vulnerable period. However, the mechanisms mediating this increased vulnerability are not known. Adolescent nicotine exposure impacts a range of adult behaviors, including increasing anxiety-like behavior and vulnerability to substance use, and these behavioral changes may indicate specific brain regions impacted by developmental nicotine exposure. Importantly, increased anxiety-like behavior may directly drive increased alcohol consumption through negative reinforcement (i.e. alcohol decreases the negative affective state caused by increased anxiety, so increased anxiety drives greater alcohol use). In this award, we are targeting two neuronal circuits that are critical for both anxiety-like and reward-related behaviors: ventral tegmental area (VTA) projections to the nucleus accumbens core (NAc) and locus coeruleus (LC)/nucleus of the solitary tract (NTS) projections to the ventral bed nucleus of the stria terminalis (vBNST). We have preliminary evidence that adolescent, but not adult, nicotine self-administration decreases dopamine release in the NAc and increases catecholamine release (likely norepinephrine) in the vBNST. Therefore, our central hypothesis is that adolescent nicotine self-administration alters the development of VTA-NAc and LC/NTS-vBNST circuits, and this dysregulation, in part, drives increased anxiety-like behaviors and vulnerability to excessive alcohol use. I will test this hypothesis using neurochemical, neurophysiological, and optogenetic techniques. In Aim I, I will identify changes to alcohol consumption and anxiety-like behaviors following adolescent or adult nicotine self-administration and examine if these relate to changes in dopamine and norepinephrine release in the NAc and vBNST. I will us both electrical and optogenetic ex vivo fast scan cyclic voltammetry in connection with behavioral measures of ethanol consumption and anxiety measures to correlate neurochemical and behavioral changes. In Aim 2, I will measure in vivo changes to neuronal activity in projections to the NAc and vBNST during ethanol consumption and anxiety-like behaviors following adolescent or adult nicotine exposure. I will then use optogenetics in awake behaving animals to normalize neuronal activity and examine how this impacts behavior.